Dielectric Vs. Resistor

  1. Hi,

    Do material posses both dielectric as well as resistance properties?

    I imagine that when there is a difference in potential across a volume of some material, some current will flow (I=V/R <-- the material's resistance), but also the material may become polarized to a certain degree (dielectric property). Is this true? Am I on the right track?

    Thanks,
     
  2. jcsd
  3. sophiecentaur

    sophiecentaur 14,131
    Science Advisor
    Gold Member

    Yes, the two are important, taken together in some materials. This is particularly important when high frequency AC is concerned and an insulating material (dielectric) is constantly being polarised in different directions. Take, for instance, a cheap Capacitor that works fine at 1MHz. The 'resistive' component of the dielectric can produce serious losses at 100MHZ or higher. (But I think this is the 'inverse' of your actual question.)
    Where DC is concerned, the valence electrons in a metal will move readily, so the electric field will be small - and, hence, the other electron orbitals will not be altered significantly (which is what is implied by 'polarisation'). In semiconductors or some impure mixtures, the internal fields when conducting DC could be enough to produce some distortion of the molecules but it would be very difficult to detect this effect at DC.
    The idea of this complex dielectric constant is essentially something relevant to AC.
     
  4. And yes from my location as well. Sophiecentaur and I seem to live in places where laws of physics show great similarities.

    One example: very pure water is used for a limited time as a dielectric, to store amazing amounts of energy. It was done in the previous version of the Z-machine (have a search, it's fun) because water has a very good breakdown field over a short time and a huge permittivity around 80, making capacitors compact. It's also cheap enough to fill a complete pool, even when de-ionized, so said capacitor, charged at several MV, makes a really nice ZAP.

    But if someone tries to keep the charge for too long, then the resistance (the conductivity) gets annoying and discharges the water capacitor.
     
  5. Thank you both. :)
     
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